Motor Control in the Brain

What is the motor system? Defined

The nerve cells that are used to control our body. Two roles: Plan, control, and execute voluntary (deliberate) movements. Control involuntary (subconscious or automatic) functions (such as digesting food).

What is the system?

Top-down process for voluntary movement. Neural activity in the frontal lobes sends commands to motor neurons in brainstem or spinal cord, which activate muscle groups. In reality, motor control is more a loop between sensory cortex and motor cortex. Ascending: from muscle to brain. Main loop: descending brain to muscle

Voluntary movement control - What brain regions are involved?

Association cortices: Important for initiation of motor control. Prefrontal cortex (PFC) and Posterior Parietal Cortex.

Prefrontal Cortex (PFC)

Initiates the long-term planning or cognitive aspects of movements. Ex. Brushing your teeth is good for hygiene and health. Determines if some motor action is appropriate for the specific situation. Experimenter tells you to click left for green light; then it switches click right for green light. Weighs the consequences of motor action & makes update about future motor actions in similar or different circumstances.

Posterior Parietal Cortex

Concerned with integrating somatosensory with visual information and determining an appropriate motor action. For example, if you were planning to get up from your seat to walk across the room, the posterior parietal cortex would take in the somatosensory proprioceptive information about how your body is positioned, and the visual information from the objects in the room to avoid running into them.

The motor cortex - posterior aspect of frontal lobe - three stuctures

Premotor area (PM), Supplemental motor area (SMA), Primary motor cortex (M1)

Premotor area (PM)

Most anterior structure. Modulates motor output; activates prior to motor activity

Supplemental motor area (SMA)

More dorsal to the PM. Also sends projections to the spinal cord. Communicates bilaterally in other words, SMA is responsible for proper communication between motor commands in both hemispheres.

Primary Motor Cortex (M1)

Posterior to SMA; borders the central sulcus. Major motor control center. Required for deliberate voluntary movements. Movements made in response to a command. Influences motor neurons: neurons that communicate down into the spinal cord and ultimately influence muscles and glands. Neurons in M1 are referred to as upper motor neurons. Lower motor neurons: found at the brainstem or spinal cord; fires whenever the upper motor neuron sends a signal.

Flow of information of what is going on in the brain

PFC/Posterior Parietal → SMA/PM → M1 → brainstem/spinal cord

Other brain areas that contribute to motor control

Frontal eye field (FEF) and Broca’s area

Frontal eye field (FEF)

Communicates with extraocular muscles and mediates saccadic eye movements

Broca’s area

Contributes to motor processes related to language (speech production).

Other brain areas that contribute to motor control

For feedback and refinement of voluntary motor control. Basal ganglia and cerebellum

Basal Ganglia

The basal ganglia are a group of brain structures linked together, handling complex processes that affect your entire body. While best known for their role in controlling your body’s ability to move, experts now know they also play a role in several other functions, such as learning, emotional processing, and more.

Cerebellum

Coordinates contraction timing and degree; smooths movements

Summary of Penfield and the Motor Homunculus

Awake neurosurgery to help with epilepsy. Stimulate portions of the cortex to induce the origin of the seizure and keep the language and hand movement areas safe. Ended up progressively moving across M1 while using an electrode to stimulate patches of cortex. 1) stimulation caused contralateral activity. (stimulating left side of brain affects muscle activity on the right side of the body). 2) different populations of neurons are responsible for communicating with specific muscle groups. (dorsal M1 activates hip and trunk; lateral M1 activates muscles on the face). Topographical organization

Topographical Organization

Refers to the orderly spatial arrangement of components within a structure, where nearby neurons or regions process information from nearby locations in the sensory or motor world. 

Clinical Application: Brain - machine interface & prosthetic limbs

Based on Penfield’s work that showed specific neurons can produce muscle activity, scientists have tried decoding these signals so they can be used to help amputees control their prosthetic limbs. Technology: Brain-machine interface. Technique: electrocorticogram (eCoG). High-density electrode capable of sensing neural activity onto the surface of M1. Can detect electrical activity at high spatial and temporal resolution.

High Spatial and Temporal Resolution meaning

High spatial resolution refers to the ability to distinguish fine details in an image, while high temporal resolution means capturing images or data at a very rapid rate, allowing for the study of fast-changing phenomena

Implanting EEG and ECoG

EEG - Detects things through scalp and skull. ECoG needs to be implanted directly on brain.